Solar energy

Nature of science:

Public understanding—harnessing the sun’s energy is a current area of research and challenges still remain. However, consumers and energy companies are being encouraged to make use of solar energy as an alternative energy source. (5.2)

• Light can be absorbed by chlorophyll and other pigments with a conjugated electronic structure.
• Photosynthesis converts light energy into chemical energy: 6CO₂ + 6H₂O --> C₆H₁₂O₆ + 6O₂
• Fermentation of glucose produces ethanol which can be used as a biofuel: C₆H₁₂O₆ --> 2C₂H₅OH + 2CO₂
• Energy content of vegetable oils is similar to that of diesel fuel but they are not used in internal combustion engines as they are too viscous.
• Transesterification between an ester and an alcohol with a strong acid or base catalyst produces a different ester:RCOOR¹ + R²OH --> RCOOR² + R¹OH
• In the transesterification process, involving a reaction with an alcohol in the presence of a strong acid or base, the triglyceride vegetable oils are converted to a mixture mainly comprising of alkyl esters and glycerol, but with some fatty acids.
• Transesterification with ethanol or methanol produces oils with lower viscosity that can be used in diesel engines.

Applications and skills:

• Identification of features of the molecules that allow them to absorb visible light.
• Explanation of the reduced viscosity of esters produced with methanol and ethanol.
• Evaluation of the advantages and disadvantages of the use of biofuels.
• Deduction of equations for transesterification reactions.

• The claims of “cold fusion” were dismissed as the results are not reproducible. Is it always possible to obtain replicable results in the natural sciences? Are reproducible results possible in other areas of knowledge?

Utilization:

• Syllabus and cross-curricular links:
• Topic 5.3—bond enthalpies
• Topic 20.1—mechanism of nuclear substitution reactions
• Biology topic 2.9—photosynthesis

Aims:

• Aim 2: The conversion of solar energy is important in a number of different technologies.
• Aim 6: Experiments could include those involving photosynthesis, fermentation and transesterification.
• Aim 8: Transesterification reactions, with waste cooking oil, could reduce waste and produce excellent biofuels.

• Only a conjugated system with alternating double bonds needs to be covered.